Marine cloud brightening has been proposed as a means of geoengineering/climate intervention, or deliberately altering the climate system to offset anthropogenic climate change. In idealized simulations that highlight contrasts between land and ocean, we find that the globe warms, including the ocean due to transport of heat from land. This study reinforces that no net energy input into the Earth system does not mean that temperature will necessarily remain unchanged.

In simulations with different climate models in which the strength of the Sun is reduced to cancel the surface warming from a quadrupling of atmospheric carbon dioxide, low cloud cover decreases, high cloud cover increases, the upper troposphere and stratosphere cool, and water vapor concentration decreases. The stratospheric cooling and low cloud reduction result in more sunlight reduction being needed than originally thought.

The aim of the presented study was to investigate the impact on the radiation budget and atmospheric dynamics of a biomass-burning plume, transported from Alaska to the High Arctic region of Ny-Ålesund, Svalbard, in early July 2015. We found that the smoke plume may significantly alter radiative properties of the atmosphere. Furthermore, the simulations of atmospheric dynamics indicated a vertical positive displacement and broadening of the plume with time.

A numerical model also used for operational weather forecast was applied to investigate the impact of contrails and contrail cirrus on the radiative fluxes at the earth's surface. Accounting for contrails produced by aircraft enables the model to simulate high clouds that are otherwise missing. In a case study, we find that the effect of these extra clouds is to reduce the incoming shortwave radiation at the surface as well as the production of photovoltaic power by up to 10 %.

One of the most important parameters in climate science is the equilibrium climate sensitivity (ECS). Estimates of this quantity based on 20th-century observations suggest low values of ECS (below 2 °C). We show that these calculations may be significantly in error. Together with other recent work on this problem, it seems probable that the ECS is larger than suggested by the 20th-century observations.

This study examines how different aerosol optical properties determine the dust longwave radiative effects at the surface, in the atmosphere and at the top of the atmosphere, based on the combination of remote sensing and in situ observations from the ground, from airborne sensors, and from space, by means of radiative transfer modelling. The closure experiment is based on longwave irradiances and spectral brightness temperatures measured during the 2013 ChArMEx–ADRIMED campaign at Lampedusa.

This paper quantifies the radiative effects of dust and water vapour in the Saharan heat low. Dust has a warming effect at the top of the atmosphere while cooling the surface. Water vapour has a warming effect both at the top of atmosphere and the surface. We find dust and water vapour have similar effects in driving the variability in the top-of-atmosphere radiative budget, while dust has a stronger effect than water vapour in controlling day-to-day variability of the surface radiative budget.

The formation of shallow cumulus cloud streets was historically attributed primarily to dynamics. Here, we focus on the interaction between radiatively induced surface heterogeneities and the resulting patterns in the flow. Our results suggest that solar radiative heating has the potential to organize clouds perpendicular to the sun's incidence angle.

This study proposes models to estimate the UVER diffuse irradiance, which means, at least, 40 % of the ultraviolet solar radiation reaching the Earth's surface at mid-latitudes. These models are inspired by expressions originally used to estimate total diffuse fraction and rely on variables commonly available to favor their applicability. The best model in this paper performs better than previous approaches and no additional information about the cloud or aerosol layer is needed.

The dependence of solar-disk and circumsolar radiances on ice cloud
properties is studied with a Monte Carlo radiative transfer model. Ice
crystal roughness (or more generally, non-ideality) is found to be the
most important parameter influencing the circumsolar radiance, and ice
crystal sizes and shapes also play significant roles. When comparing
with radiances measured with the SAM instrument, rough ice crystals
reproduce the measurements better than idealized smooth ice crystals do.

Radiation is driving weather and climate. Yet, the effect of radiation on clouds is not fully understood and often only poorly represented in models. Better understanding and better parameterizations of the radiation–cloud interaction are therefore essential. Using our newly developed fast neighboring column approximation for 3-D thermal heating and cooling rates, we show that thermal radiation changes cloud circulation and causes organization and a deepening of the clouds.

This study uses global climate models to quantify how strongly man-made emissions of selected pollutants modify the energy budget of the Earth. The pollutants studied interact directly and indirectly with sunlight and terrestrial radiation and remain a relatively short time in the atmosphere, leading to regional and seasonal variations in their impacts. This new data set is useful to compare the potential climate impacts of different pollutants in support of policies to reduce climate change.

The radiative effects of spatially complex cloud fields are notoriously difficult to estimate and are afflicted with errors up to ±50 % of the incident solar radiation. We find that horizontal photon transport, the leading cause for these three-dimensional effects, manifests itself through a spectral fingerprint – a new observable that holds promise for reducing the errors associated with spatial complexity by moving the problem to the spectral dimension.

This article presents a comparison between the two surface-UV dose series, measured with Brewer spectrophotometers working simultaneously at two different sites in Poland: in a large city agglomeration and in the suburbs. We consider whether the city of Warsaw acts as a shield from ultraviolet overexposure. Our study proves that the UV level in Warsaw is slightly lower than that found in cleaner suburbs of the city.

Air pollution can reach distant regions through intercontinental transport. Here we first present results from the Hemispheric Transport of Air Pollution Phase 2 exercise, where many models performed the same set of coordinated emission-reduction experiments. We find that mitigations have considerable extra-regional effects, and show that this is particularly true for black carbon emissions, as long-range transport elevates aerosols to higher levels where their radiative influence is stronger.

Biologically active ultraviolet (UV) radiation is an important environmental factor, which affect human health and nature. UV radiation has a significant increase with the altitude. We propose a new method for calculating the altitude UV dependence for different types of biologically active UV radiation. The proposed method was implemented in the on-line UV tool (http://momsu.ru/uv/) for Northern Eurasia. The possible UV effects on human health were considered over Alpine zone.

This paper documents a new package for the Weather Research and Forecasting--Advanced Research WRF (WRF-ARW) model that can simulate any partial, total or hybrid solar eclipse for the period 1950–2050 and is also extensible to a longer period. First, a description of the implementation together with a validation for the period 1950–2050 of all solar eclipse trajectories is presented. Second, the model response is analyzed in four total solar eclipse episodes. Global horizontal irradiance (GHI) outcomes are validated with respect to ground-based measurements.

We examine the impact of buildings on surface solar fluxes in Beijing by accounting for their 3-D structures. We find that inclusion of buildings changes surface solar fluxes by within ±1 W m−2, ±1–10 W m−2, and up to ±100 W m−2 at grid resolutions of 4 km, 800 m, and 90 m, respectively. We can resolve pairs of positive-negative flux deviations on different sides of buildings at ≤ 800 m resolutions. We should treat building-effect on solar fluxes differently in models with different resolutions.

We performed an irradiance forecast experiment based on analysis of
hemispheric sky images and evaluated results on a large data set of 99
pyranometers distributed over 10 × 12 km. We developed a surface
irradiance retrieval from cloud information derived from the images.
Very high resolution forecasts were processed up to 25 min. A main
finding is that forecast skill is enhanced in complex cloud conditions
leading to high variability in surface irradiance.

It is shown here that RegCM4 regional climate model adequately simulates surface solar radiation (SSR) over Europe but significantly over/underestimates several parameters that determine the transmission of solar radiation in the atmosphere. The agreement between RegCM4 and satellite-based SSR observations is actually a result of the conflicting effect of these parameters. We suggest that there should be a reassessment of the way these parameters are represented within this and other models.

This paper investigates 3-D mountain effects on solar flux distributions and their impact on surface hydrology over the western United States, specifically the Rocky Mountains and the Sierra Nevada, using the global CCSM4 (CAM4/CLM4) with a 0.23°×0.31° resolution for simulations over 6 years. We show that deviations in the net surface fluxes are not only affected by 3-D mountains but also influenced by feedbacks of cloud and snow in association with the long-term simulations.

This study examines quantitatively the impact of methodological choices, in particular of averaging of multi-model ensembles, on climate metrics for ozone precursors.
Estimates of the standard deviation of radiative forcing (RF), global warming and temperature potential (GWP, GTP) from ensemble-mean input fields generally overestimate the true value.
The multi-model average fields are appropriate for calculating mean metrics, but are not a reliable method for calculating the uncertainty.

This paper develops two models for the reconstruction of ultraviolet erythemal radiation (UVER). The models are based on shortwave radiation (SW) and sunshine duration measurements. Both models are used to reconstruct UVER irradiation at nine Spanish places from 1950 to 2011. The trends of UVER are calculated at different periods. UVER presented a brightening phenomenon, but not dimming, due to the ozone depletion until the mid-1990s.

The impact of cities and urban surfaces on climate of central Europe is examined using a regional climate model coupled to a single-layer urban canopy model. Results show a significant impact on temperature (up to 1.5K increase in summer), the boundary layer height, surface wind with a winter decrease and precipitation (a summer decrease). Applying the urban canopy model, the regional climate model exhibits a decreased model bias when compared to observations.